A thermal insulator is a material that resists the transfer of heat. It is used to reduce the transfer of heat between two objects or surfaces. Thermal insulators are used in a wide variety of applications, including buildings, appliances, and clothing.

Some common thermal insulators include:

- Fiberglass is a lightweight material made from glass fibers. It is commonly used as an insulation material in buildings and appliances.

- Cellulose is a natural fiber made from plant material. It is used as an insulation material in buildings and furniture.

- Polystyrene is a synthetic plastic material. It is commonly used as an insulation material in buildings and packaging.

- Polyethylene is a synthetic plastic material. It is commonly used as an insulation material in packaging and clothing.

- Polyurethane is a synthetic plastic material. It is commonly used as an insulation material in buildings and appliances.

The effectiveness of a thermal insulator is measured by its R-value. The R-value is the measure of the resistance to heat flow of a material. The higher the R-value, the more effective the insulation material is at preventing heat transfer.